1. Field of the Invention
The present invention relates to a linear actuator, and a pump device and a compressor device using the linear actuator.
2. Description of Related Art
A linear actuator, which is used in a pump device or a compressor device with a piston linearly moving within a cylinder, commonly uses a motor outputting a rotational movement. Therefore, a crankshaft is used between the output shaft of the motor and the piston to convert the rotational movement into a linear movement by using the crankshaft. Accordingly, the transmission efficiency of force is low.
Alternatively, as shown in FIG. 5, a linear actuator has been known which includes an inner yoke 103, an outer yoke 104, a coil 108 and a movable body 106. The outer yoke 104 is disposed so as to face the inner yoke 103 with a predetermined gap space in a direction perpendicular to an axial direction which is the moving direction of the movable body 106. A first gap space 109A and a second gap space 109B are formed between the inner yoke 103 and the outer yoke 104. The coil 108 is used to generate the alternating magnetic field whose magnetic path is formed by the outer yoke 104, the first gap space 109A, the inner yoke 103 and the second gap space 109B. The movable body 106 disposed between the inner yoke 103 and the outer yoke 104 is alternately driven in the axial direction by the alternating magnetic field.
However, in the linear actuator constituted as shown in FIG. 5, the facing portions of the outer yoke 104 to the inner yoke 103 may be displaced by the attraction force of the movable body, i.e., a magnet 106 to cause to be brought into contact with the magnet 106. In addition, whenever the magnet 106 moves in the axial direction, the portion of the facing portions of the outer yoke 104 which is attracted by the magnet 106 is counterchanged alternately. Therefore, when the magnet 106 is driven and moved alternately in the axial direction at a high speed as in the case used in a pump device or a compressor device, the magnetic vibration may occur.